Electronic vapour provision system

ABSTRACT

An electronic vapor provision system includes a vaporizer for vaporising liquid for inhalation by a user of the electronic vapor provision system; a power supply comprising a cell or battery for supplying power to the vaporizer; a sensor for measuring the rate of airflow through the electronic vapor provision system as a result of the inhalation by the user; and a control unit for controlling the power supplied to the vaporizer based on a cumulative airflow for this inhalation by the user, wherein the cumulative airflow is determined based on the measurements of airflow rate by the sensor. Such a system allows the user control over the amount of vaporized liquid obtained in a given inhalation based on the cumulative airflow for the given inhalation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Phase entry of PCT Application No.PCT/GB2015/050958, filed on 30 Mar. 2015, which claims priority to GBPatent Application No. 1410171.1, filed on 9 Jun. 2014, which are herebyfully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to electronic vapor provision systemssuch as electronic nicotine delivery systems (e.g. e-cigarettes).

BACKGROUND

Electronic vapor provision systems such as e-cigarettes generallycontain a reservoir of liquid, typically nicotine, which is to bevaporized or otherwise converted into an aerosol. For example, when auser inhales on the device, a heater is activated to vaporize a smallamount of liquid, which is therefore inhaled by the user. Moreparticularly, such devices are usually provided with one or more airinlet holes located away from the mouthpiece. When a user sucks on themouthpiece, air is drawn in through the inlet holes and past the vaporsource, such as the heater supplied with nicotine or other liquid from acartridge.

The amount of power provided to the heater may be controlled foroperational reasons. For example, WO 2012/109371 describes a devicewhich has different operating modes, and the selection of operating modedepends on the interval between successive puffs (since for a shortinterval, the heater may already be warm from a previous puff). WO2013/060784 describes a device which reduces the power supplied to theheater towards the end of an inhalation in order to reduce unwantedcondensation of aerosol within the device.

In some known devices, the user can exercise a certain degree of controlover the operation of an electronic vapor provision system. Such controlmay, for example, allow a user to alter the power delivered to theheater by rotating a dial. However, existing mechanisms for controllinga user experience are still somewhat limited in terms of flexibility,responsiveness and ease of use.

SUMMARY

An electronic vapor provision system includes a vaporizer for vaporizingliquid for inhalation by a user of the electronic vapor provisionsystem; a power supply comprising a cell or battery for supplying powerto the vaporizer; a sensor for measuring the rate of airflow through theelectronic vapor provision system as a result of the inhalation by theuser; and a control unit for controlling the power supplied to thevaporizer based on a cumulative airflow for this inhalation by the user,wherein the cumulative airflow is determined based on the measurementsof airflow rate by the sensor. Such a system allows the user controlover the amount of vaporized liquid obtained in a given inhalation basedon the cumulative airflow for the given inhalation.

The approach described herein is not restricted to specific embodimentssuch as set out below, but includes and contemplates any appropriatecombinations of features presented herein. For example, an electronicvapor provision system may be provided in accordance with the approachdescribed herein which includes any one or more of the various featuresdescribed below as appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the disclosure will now be described in detail byway of example only with reference to the following drawings:

FIG. 1 is a schematic (exploded) diagram of an electronic vaporprovision system such as an e-cigarette in accordance with someembodiments of the disclosure.

FIG. 2 is a schematic diagram of the body of the e-cigarette of FIG. 1in accordance with some embodiments of the disclosure.

FIG. 3 is a schematic diagram of the vaporizer portion of thee-cigarette of FIG. 1 in accordance with some embodiments of thedisclosure.

FIG. 4 is a schematic diagram showing certain aspects of one end of thebody portion of the e-cigarette of FIG. 1 in accordance with someembodiments of the disclosure.

FIG. 5 is a schematic diagram of the main functional components of thebody of the e-cigarette of FIG. 1 in accordance with some embodiments ofthe disclosure.

FIG. 6 is a schematic flowchart which illustrates certain aspects ofoperation of the e-cigarette of FIG. 1 in accordance with someembodiments of the disclosure.

FIG. 7 is a graph showing some results corresponding to the approachshown in FIG. 6 in accordance with some embodiments of the disclosure.

DETAILED DESCRIPTION

As described above, the present disclosure relates to an electronicvapor provision system, such as an e-cigarette. Throughout the followingdescription the term “e-cigarette” is used; however, this term may beused interchangeably with electronic vapor provision system.

FIG. 1 is a schematic diagram of an electronic vapor provision systemsuch as an e-cigarette 10 in accordance with some embodiments of thedisclosure (not to scale). The e-cigarette has a generally cylindricalshape, extending along a longitudinal axis indicated by dashed line LA,and comprises two main components, namely a body 20 and a cartomizer 30.The cartomizer includes an internal chamber containing a reservoir ofnicotine, a vaporizer (such as a heater), and a mouthpiece 35. Thereservoir may be a foam matrix or any other structure for retaining thenicotine until such time that it is required to be delivered to thevaporizer. The cartomizer 30 also includes a heater for vaporizing thenicotine and may further include a wick or similar facility to transporta small amount of nicotine from the reservoir to a heating location onor adjacent the heater.

The body 20 includes a re-chargeable cell or battery to provide power tothe e-cigarette 10 and a circuit board for generally controlling thee-cigarette. When the heater receives power from the battery, ascontrolled by the circuit board, the heater vaporizes the nicotine andthis vapor is then inhaled by a user through the mouthpiece.

The body 20 and cartomizer 30 are detachable from one another byseparating in a direction parallel to the longitudinal axis LA, as shownin FIG. 1, but are joined together when the device 10 is in use by aconnection, indicated schematically in FIG. 1 as 25A and 25B, to providemechanical and electrical connectivity between the body 20 and thecartomizer 30. The electrical connector on the body 20 that is used toconnect to the cartomizer also serves as a socket for connecting acharging device (not shown) when the body is detached from thecartomizer 30. The other end of the charging device can be plugged intoa USB socket to re-charge the cell in the body of the e-cigarette. Inother implementations, a cable may be provided for direct connectionbetween the electrical connector on the body and a USB socket.

The e-cigarette 10 is provided with one or more holes (not shown inFIG. 1) for air inlet. These holes connect to an air passage through thee-cigarette 10 to the mouthpiece 35. When a user inhales through themouthpiece 35, air is drawn into this air passage through the one ormore air inlet holes, which are suitably located on the outside of thee-cigarette. This airflow (or the resulting change in pressure) isdetected by a pressure sensor that in turn activates the heater tovaporize the nicotine from the cartridge. The airflow passes through,and combines with, the nicotine vapor, and this combination of airflowand nicotine vapor then passes out of the mouthpiece 35 to be inhaled bya user. The cartomizer 30 may be detached from the body 20 and disposedof when the supply of nicotine is exhausted (and replaced with anothercartomizer if so desired).

It will be appreciated that the e-cigarette 10 shown in FIG. 1 ispresented by way of example, and various other implementations can beadopted. For example, in some embodiments, the cartomizer 30 is providedas two separable components, namely a cartridge comprising the nicotinereservoir and mouthpiece (which can be replaced when the nicotine fromthe reservoir is exhausted), and a vaporizer comprising a heater (whichis generally retained). As another example, the charging facility mayconnect to an additional or alternative power source, such as a carcigarette lighter.

FIG. 2 is a schematic (simplified) diagram of the body 20 of thee-cigarette of FIG. 1 in accordance with some embodiments of thedisclosure. FIG. 2 can generally be regarded as a cross-section in aplane through the longitudinal axis LA of the e-cigarette. Note thatvarious components and details of the body, e.g. such as wiring and morecomplex shaping, have been omitted from FIG. 2 for reasons of clarity.

As shown in FIG. 2, the body 20 includes a battery or cell 210 forpowering the e-cigarette 10, as well as a chip, such as an applicationspecific integrated circuit (ASIC) or microcontroller for controllingthe e-cigarette 10. The ASIC may be positioned alongside or at one endof the battery 210. The ASIC is attached to a sensor unit 215 to detectan inhalation on mouthpiece 35 (or alternatively the sensor unit 215 maybe provided on the ASIC itself). In response to such a detection, theASIC provides power from the battery or cell 210 to a heater in thecartomizer 30 to vaporize nicotine into the airflow which is inhaled bya user.

The body further includes a cap 225 to seal and protect the far (distal)end of the e-cigarette. There is an air inlet hole provided in oradjacent to the cap 225 to allow air to enter the body and flow past thesensor unit 215 when a user inhales on the mouthpiece 35. This airflowtherefore allows the sensor unit 215 to detect the user inhalation.

At the opposite end of the body 20 from the cap 225 is the connector 25Bfor joining the body 20 to the cartomizer 30. The connector 25B providesmechanical and electrical connectivity between the body 20 and thecartomizer 30. The connector 25B includes a body connector 240, which ismetallic (silver-plated in some embodiments) to serve as one terminalfor electrical connection (positive or negative) to the cartomizer 30.The connector 25B further includes an electrical contact 250 to providea second terminal for electrical connection to the cartomizer 30 ofopposite polarity to the first terminal, namely body connector 240. Theelectrical contact 250 is mounted on a coil spring 255. When the body 20is attached to the cartomizer 30, the connector 25A on the cartomizer 30pushes against the electrical contact 250 in such a manner as tocompress the coil spring in an axial direction, i.e. in a directionparallel to (co-aligned with) the longitudinal axis LA. In view of theresilient nature of the spring 255, this compression biases the spring255 to expand, which has the effect of pushing the electrical contact250 firmly against connector 25A, thereby helping to ensure goodelectrical connectivity between the body 20 and the cartomizer 30. Thebody connector 240 and the electrical contact 250 are separated by atrestle 260, which is made of a non-conductor (such as plastic) toprovide good insulation between the two electrical terminals. Thetrestle 260 is shaped to assist with the mutual mechanical engagement ofconnectors 25A and 25B.

FIG. 3 is a schematic diagram of the cartomizer 30 of the e-cigarette ofFIG. 1 in accordance with some embodiments of the disclosure. FIG. 3 cangenerally be regarded as a cross-section in a plane through thelongitudinal axis LA of the e-cigarette. Note that various componentsand details of the body, e.g. such as wiring and more complex shaping,have been omitted from FIG. 3 for reasons of clarity.

The cartomizer 30 includes an air passage 355 extending along thecentral (longitudinal) axis of the cartomizer 30 from the mouthpiece 35to the connector 25A for joining the cartomizer 30 to the body 20. Areservoir of nicotine 360 is provided around the air passage 335. Thisreservoir 360 may be implemented, for example, by providing cotton orfoam soaked in nicotine. The cartomizer 30 also includes a heater 365for heating nicotine from reservoir 360 to generate nicotine vapor toflow through air passage 355 and out through mouthpiece 35 in responseto a user inhaling on the e-cigarette 10. The heater 365 is poweredthrough lines 366 and 367, which are in turn connected to opposingpolarities (positive and negative, or vice versa) of the battery 210 viaconnector 25A (the details of the wiring between the power lines 366 and367 and connector 25A are omitted from FIG. 3).

The connector 25A includes an inner electrode 375, which may besilver-plated or made of some other suitable metal. When the cartomizer30 is connected to the body 20, the inner electrode 375 contacts theelectrical contact 250 of the body 20 to provide a first electrical pathbetween the cartomizer 30 and the body. In particular, as the connectors25A and 25B are engaged, the inner electrode 375 pushes against theelectrical contact 250 so as to compress the coil spring 255, therebyhelping to ensure good electrical contact between the inner electrode375 and the electrical contact 250.

The inner electrode 375 is surrounded by an insulating ring 372, whichmay be made of plastic, rubber, silicone, or any other suitablematerial. The insulating ring 372 is surrounded by the cartomizerconnector 370, which may be silver-plated or made of some other suitablemetal or conducting material. When the cartomizer 30 is connected to thebody 20, the cartomizer connector 370 contacts the body connector 240 ofthe body 20 to provide a second electrical path between the cartomizer30 and the body 20. In other words, the inner electrode 375 and thecartomizer connector 370 serve as positive and negative terminals (orvice versa) for supplying power from the battery 210 in the body to theheater 365 in the cartomizer 30 via supply lines 366 and 367 asappropriate.

The cartomizer connector 370 is provided with two lugs or tabs 380A,380B, which extend in opposite directions away from the longitudinalaxis of the e-cigarette. These tabs are used to provide a bayonetfitting in conjunction with the body connector 240 for connecting thecartomizer 30 to the body 20. This bayonet fitting provides a secure androbust connection between the cartomizer 30 and the body 20, so that thecartomizer 30 and body 20 are held in a fixed position relative to oneanother, without wobble or flexing, and the likelihood of any accidentaldisconnection is very small. At the same time, the bayonet fittingprovides simple and rapid connection and disconnection by an insertionfollowed by a rotation for connection, and a rotation (in the reversedirection) followed by withdrawal for disconnection. It will beappreciated that other embodiments may use a different form ofconnection between the body 20 and the cartomizer 30, such as a snap fitor a screw connection.

FIG. 4 is a schematic diagram of certain details of the connector 25B atthe end of the body 20 in accordance with some embodiments of thedisclosure (but omitting for clarity most of the internal structure ofthe connector as shown in FIG. 2, such as trestle 260). In particular,FIG. 4 shows the external housing 201 of the body 20, which generallyhas the form of a cylindrical tube. This external housing 201 maycomprise, for example, an inner tube of metal with an outer covering ofpaper or similar.

The body connector 240 extends from this external housing 201 of thebody 20. The body connector as shown in FIG. 4 comprises two mainportions, a shaft portion 241 in the shape of a hollow cylindrical tube,which is sized to fit just inside the external housing 201 of the body20, and a lip portion 242 which is directed in a radially outwarddirection, away from the main longitudinal axis (LA) of the e-cigarette.Surrounding the shaft portion 241 of the body connector 240, where theshaft portion does not overlap with the external housing 201, is acollar or sleeve 290, which is again in a shape of a cylindrical tube.The collar 290 is retained between the lip portion 242 of the bodyconnector 240 and the external housing 201 of the body 20, whichtogether prevent movement of the collar 290 in an axial direction (i.e.parallel to axis LA). However, collar 290 is free to rotate around theshaft portion 241 (and hence also axis LA).

As mentioned above, the cap 225 is provided with an air inlet hole toallow air to flow past sensor 215 when a user inhales on the mouthpiece35. However, the majority of air that enters the device when a userinhales flows through collar 290 and body connector 240 as indicated bythe two arrows in FIG. 4.

FIG. 5 is a schematic diagram of the main functional components of thebody 20 of the e-cigarette 10 of FIG. 1 in accordance with someembodiments of the disclosure. These components may be mounted on thecircuit board provided within the body 20, although depending on theparticular configuration, in some embodiments, one or more of thecomponents may instead be accommodated in the body 20 to operate inconjunction with the circuit board, but is/are not physically mounted onthe circuit board itself The body 20 includes the sensor unit 215located in or adjacent to the air path through the body 20 from the airinlet to the air outlet (to the vaporizer). The sensor unit 215 includesa pressure drop sensor 562 and temperature sensor 563 (also in oradjacent to this air path). The body 20 further includes a small speaker558 and an electrical socket or connector 5B for connecting to thecartomizer 30 or to a USB charging device.

The microcontroller (e.g. an ASIC) 555 includes a CPU 550. Theoperations of the CPU 550 and other electronic components, such as thepressure sensor 562, are generally controlled at least in part bysoftware programs running on the CPU 550 (or other component). Suchsoftware programs may be stored in non-volatile memory, such as ROM,which can be integrated into the microcontroller 555 itself, or providedas a separate component. The CPU 550 may access the ROM to load andexecute individual software programs as and when required. Themicrocontroller 555 also contains appropriate communications interfaces(and control software) for communicating as appropriate with otherdevices in the body 20, such as the pressure sensor 562.

The CPU 550 controls the speaker 558 to produce audio output to reflectconditions or states within the e-cigarette 10, such as a low batterywarning. Different signals for signaling different states or conditionsmay be provided by utilizing tones or beeps of different pitch and/orduration, and/or by providing multiple such beeps or tones.

As noted above, the e-cigarette 10 provides an air path from the airinlet through the e-cigarette 10, past the pressure drop sensor 562 andthe heater (in the vaporizer or cartomizer 30), to the mouthpiece 35.Thus when a user inhales on the mouthpiece of the e-cigarette 10, theCPU 550 detects such inhalation based on information from the pressuredrop sensor. In response to such a detection, the CPU 550 supplies powerfrom the battery or cell 210 to the heater, which thereby heats andvaporizes the nicotine from the wick for inhalation by the user.

The e-cigarette 10 is configured to respond to a puff (inhalation) froma user or consumer, such that the amount and/or quality of the vaporgenerated is controllable by the consumer based on the puff effortand/or puff volume. This is somewhat similar to the situation with aconventional combustible cigarette, which responds to a consumer's puffwith total particulate matter (TPM) being roughly proportional to puffvolume (for a particular cigarette type). Accordingly, the puff effortor cumulative puff volume for a given inhalation is measured in thee-cigarette 10 using sensor unit 215, and the microcontroller 555 isconfigured so that e-cigarette 10 responds to the measured puff volumeor effort by delivering more/less vapor (as appropriate) and/or adifferent quality of vapor. This gives a consumer an intuitive way tocontrol their use of the e-cigarette 10 in terms of vapor production,etc.

FIG. 6 is a schematic flowchart which illustrates certain aspects ofoperation of the e-cigarette of FIG. 1 in accordance with someembodiments of the invention to provide such user control based on puffvolume or effort. Processing commences with the detection of the startof a user inhalation (puff) at operation 610. Such a detection is madeby sensor unit 215, in particular, pressure sensor 562, which detectsthe drop in pressure caused by the user sucking on the mouthpiece 35. Inaddition, using the measured pressure drop, once an inhalation has beendetected, the airflow rate through the e-cigarette can be determined(operation 620). A more accurate determination can generally be made ifthe temperature of the airflow is also included (since the density ofair is temperature dependent). Therefore, such a temperature may bemeasured at the same time as the pressure drop (such as by using thetemperature sensor 563 included in sensor unit 215, see FIG. 5) and thismeasured temperature can be incorporated into the determination of theairflow. If the sensor unit does not include a temperature sensor, thena fixed (average) temperature may be assumed.

The relationship between pressure drop and airflow rate (andtemperature, if available) may be determined empirically and/or bycalculation/modeling. In the former case, the e-cigarette 10 can beplaced in a mechanical device that simulates inhalation through themouthpiece. This then allows measurements of airflow through themouthpiece against pressure drop (as determined by the pressure sensor562), including temperature sensitivity if so desired, thereby allowingan empirical relationship between the two to be developed.Alternatively, the relationship between pressure drop and airflow ratemay be modeled based on the known internal shape of the e-cigarette,using fluid dynamics, etc. The resulting relationship between pressuredrop and airflow rate (and temperature, if available), whetherdetermined empirically or by calculation/modeling (or by a combinationof the two) can then be provided to the microcontroller 555, either ascode implementing a suitable mathematical expression corresponding tothe relationship, or as suitable set of data values, e.g. in the form ofa lookup table stored in some ROM in, or at least accessible to, themicrocontroller 555. This relationship allows the microcontroller 555 todetermine the current airflow rate based on the measured pressure dropfrom pressure sensor 562.

In other implementations, the sensor unit 215 may include an airflowmonitor to directly measure airflow (rather than pressure drop). In suchimplementations, it may still be desirable to determine empiricallyand/or by calculation/modeling the relationship between the airflowmeasured by this monitor and the actual volume inhaled by a user.

Having measured and determined the current airflow at operation 620, thetotal or cumulative airflow for this puff or inhalation is nowdetermined (operation 630). This cumulative airflow can be determined ineffect by summing or integrating the current (instantaneous) airflow asmeasured at operation 620 for the duration of the inhalation (so far).

The e-cigarette 10 now uses the cumulative inhalation volume so far forthis particular puff to control the vapor output in this same puff(operation 640). In other words, the e-cigarette supports an adaptive,real-time control facility for modifying the vapor output to the userthrough the mouthpiece 35. This control may be exercised in a variety ofways, for example:

-   -   delivering an amount of aerosol (vapor) which is proportional to        cumulative airflow    -   delivering an amount of aerosol (vapor) which is proportional to        some other, e.g. non-linear, function of cumulative airflow,        such as following an exponential or logarithmic relationship    -   adjusting a mix of flavors with the aerosol (vapor) based on        cumulative airflow.    -   adjusting a particle size within the aerosol (vapor) based on        cumulative airflow.

The above possibilities are provided by way of example only, and furtherways for controlling the vapor output of the e-cigarette 10 inaccordance with the cumulative airflow volume (so far) will be apparentto the skilled person.

The microcontroller 555 is generally responsible for implementing thedesired control of vapor output based on the measured cumulative airflowfor the current puff. For example, the microcontroller 555 may increase(or decrease) the power supplied to the heater 365 in order to increase(or decrease) the production rate of vapor or aerosol. In someimplementations, such power control may be implemented by altering thecurrent (and/or voltage) supplied to the heater 365. Other embodimentsmay use a different approach, such as pulse width modulation (PWM). Inthe PWM, a pulse of electrical power is delivered to the heater everytime period or window Tw, where Tw is selected to be relatively short,so that the heater does not change significantly in temperature duringthe interval Tw (without receiving any power). The duration of the pulseitself, Tp, is selected to occupy a fraction (or potentially all) of thetime window, i.e. Tw≧Tp. The amount of power provided (on average) tothe heater can be controlled by adjusting Tp, with the maximum provisionof power occurring when Tp=Tw.

In some implementations, the heater 365 may comprise multiple differentelements which can be separately controlled, with different flavorsvaporized by different heater elements. This then allows themicrocontroller to alter the mix of flavors within the output from thee-cigarette by varying the power supplied to the different heaterelements according to the desired mix of flavors.

The processing of FIG. 6 now makes a determination as to whether or notthe inhalation is over (operation 660)—this can be detected by theabsence of any pressure drop across the pressure sensor unit 562. If theinhalation is over, this represents the end of the processing for thisparticular puff. Alternatively, if a pressure drop is still detected,hence the inhalation is still ongoing, the processing cycles back tooperation 620. The e-cigarette 10 then measures again the airflow of theinhalation and uses this measurement to update the cumulative puffvolume so far (operation 630). This then allows the determination of theaerosol amount and the heater control to be updated accordingly atoperations 640 and 650 respectively. This processing loop then continuesas before until the inhalation is finally over, as detected at operation660.

FIG. 7 is a graph showing an example of controlling the power to aheater 365 with a view to delivering a cumulative amount of aerosol thatmatches (corresponds to) the cumulative puff volume using a linear(proportionality) relationship in the course of a single inhalation.There are four lines plotted in FIG. 7 which are as follows:

-   -   a) puff flow—i.e. current rate of airflow being inhaled by the        user (light, dashed line)    -   b) cumulative airflow—in effect, the integral of (a),        representing the total amount of airflow for this puff (dark,        solid line)    -   c) power supplied to the heater—(light, solid line)    -   d) cumulative output of vapor, in effect, the total volume of        vapor output so far this puff.        The X-axis of FIG. 7 is time (seconds), while the scale of the        Y-axis represents the power level supplied to the heater as a        function of the maximum available power supply to the        heater—i.e. as per line (c) above. (The scaling on the Y-axis        for the other three lines depicted in FIG. 7 is arbitrary.)

The amount of aerosol or vapor delivered by the e-cigarette is dependenton various factors, especially the power delivered to the heater 365,expected temperature of the heater 365 (which is itself related to thepower delivered to the heater 365), expected temperature loss from theheater 365 due to convention & radiation, and temperature loss due toevaporation of the formulation, i.e. the nicotine or other liquid to bevaporized. The aerosol delivered is generally proportional to thetemperature loss due to formulation evaporation.

As shown in FIG. 7, when a puff is detected (corresponding to operation610 in FIG. 6), the power to the heater 365 is set initially to 100% tobring the e-cigarette 10 up to an active temperature (as per line (c)).At this stage, the puff airflow (line (a)) is increasing steadily. Thisreflects the motion of the lungs of the user, which have to beaccelerated from an initial rest position. As the lungs accelerate togreater speed, so the airflow of the inhalation increases.

In the particular example of FIG. 7, the microcontroller 555 is taskedwith having the cumulative vapor output match (track) the cumulativeairflow output. It will be appreciated that this leads to anapproximately constant proportion of vapor within the airflow—so thatwhen the user inhales most strongly to produce the greatest airflow, theamount of vapor inhaled (in absolute terms) is likewise at a maximum.

At the beginning, the cumulative puff airflow (line (b)) goes ahead ofthe cumulative vapor output (line (d)), because of the delay inproducing vapor while the heater temperature is raised to itsoperational point. Once this has occurred, after about 0.5 seconds inFIG. 7, vapor starts being produced. At this point, the vapor output,and hence the cumulative vapor output (line (d)), rise rapidly, ineffect catching up with the cumulative airflow (line (b)).

The power to the heater 365 now drops to avoid overheating. However, asthe airflow past the heater 365 increases (as indicated by line (a)),this allows the heater 365 to vaporize more liquid (since the increasedairflow draws the previously vaporized liquid out of the e-cigarette10). This then leads to increased power requirements for the heater 365,and hence a rise in the power supply to the heater 365 just before 1 s.

Over the next second, the rate of increase in the airflow (line (a))starts to decrease, and then eventually the airflow rate itself peaksand starts to fall. The heater power (line (c)) likewise peaks and thenstarts to fall in this period. Finally, in the last second of theinhalation (from 2 s to 3 s), the airflow rate of the inhalationsteadily declines back down to zero, and again the heater power (line(c)) shows a generally similar decrease.

In terms of control theory, we can represent the rate of vapor output asV(t) and the power input to the heater as P(t), such that V(t)=H(P(t)),where H is a transfer function based on factors discussed above, such aspreviously supplied power to the heater, loss of heat from the heaterdue to vapor production, etc. If the measured airflow rate is A(t), thenthe overall objective for the microcontroller is that F1(V(t))=F2(A(t)), where F1 and F2 are functions to be specified and may include atiming offset between the measured airflow (input) rate and the vaporoutput. Taking the example of FIG. 7, this corresponds to having F1 andF2 such that:

∫₀ ^(t) V(t)=k∫ ₀ ^(t) A(t)

where k is a constant, and the puff is assumed to start at t=0, so thatthe left hand side represents the cumulative vapor output for this puff,while the right hand side represents the cumulative airflow into (andthrough) the system for this puff.

Writing H⁻¹ as the inverse of H, and F3=F1 ⁻¹(F2), where F⁻¹ is likewisethe inverse of F, then V(t)=F3(A(t)), and P(t)=H⁻¹(V(0), and wetherefore have P(t)=H⁻¹(F3(A(0)). It will be appreciated that thisequation can be used by the microcontroller 555 to determine the powerinput to the heater based on (i) the measured airflow rate A(t), (ii)the desired relationship between the airflow rate and the vapor outputrate V(t), as represented by the function F3, and (iii) the relationshipbetween the power input to the heater 365 and the vapor output rate, asrepresented by the transfer function H (and its inverse H⁻¹).

As described herein, various embodiments provide an electronic vaporprovision system including a vaporizer for vaporizing liquid forinhalation by a user of the electronic vapor provision system, a powersupply comprising a cell or battery for supplying power to thevaporizer; a sensor for measuring the rate of airflow through theelectronic vapor provision system as a result of the inhalation by theuser; and a control unit. The control unit controls the power suppliedto the vaporizer based on a cumulative airflow for this inhalation bythe user, wherein the cumulative airflow is determined based on themeasurements of airflow rate by the sensor. This allows the user controlover the amount of vaporized liquid obtained in a given inhalation basedon the cumulative airflow produced by the given inhalation.

It will be appreciated that the detailed nature of the control may varyfrom one implementation to another. For example, as described above, thecontrol may be configured so that the cumulative vapor output, i.e. theoverall (cumulative) amount of vaporized liquid for this inhalation,tracks the cumulative airflow through the device. Another possibility(for example) is that for a higher cumulative airflow, an additionalheater element is activated. This may increase vapor output, or changethe mix of vapor output, such as by altering the relative amounts of twodifferent vapors in the vapor output.

The cumulative airflow represents the total volume of air that haspassed into (through) the system so far, since the start of theinhalation. The start of the inhalation may be detected by the airflowsensor, which also then measures the current (instantaneous) airflowrate during the inhalation. The cumulative airflow can then bedetermined, for example, by integrating the measured current airflowfrom the start of the inhalation to the present stage of the inhalation.Another possible mechanism for determining the cumulative airflow is tomeasure the current or instantaneous airflow rate at multiple times, andthen perform some modeling or lookup to determine the cumulativeairflow. For example, the control of the vapor output may be based inpart on a predicted airflow value—e.g. based on the cumulative airflowmeasured already for that particular inhalation and/or multipleinstantaneous measurements of airflow, plus knowledge of a typicalairflow rate variation with time (i.e. corresponding to line (a) in FIG.7).

When additional measurements of the actual airflow are obtained, thesecan be compared with the predicted airflow rate, and any discrepancyused to adjust the future power supply to the heater. In some cases, thepredicted airflow rate may be based on measured airflow rates forprevious inhalations by that user. The use of a predicted airflow ratein this manner may help to improve the responsiveness of the control.

The cumulative airflow may be determined within the sensor itself,within the control unit, or within any other appropriate component ofthe electronic vapor provision system. The cumulative airflow may bedetermined explicitly or implicitly, using one or more other parametersthat serve in effect as a proxy for the cumulative airflow. For example,the senor may measure pressure drop, which may then be converted into aparameter that reflects the cumulative airflow (and hence can be usedfor controlling the power to the heater) without explicitly determiningthe cumulative airflow per se.

As described herein, a user can therefore control, at least in part, thevapor they receive. This control can be provided in an intuitive manner,e.g. just by puffing (inhaling) harder for more vapor, or by puffingsoftly for less vapor. The intuitive nature of the control is enhancedits rapid (real-time) responsiveness, in other words, if the userchanges the puff (inhalation) rate during an individual puff, thisproduces a noticeable change in vapor output even during the same puff.For example, with reference to FIG. 7, we can see that the timeresponsiveness of the system is a small fraction of 1 s, typically lessthan 0.5 seconds, or less than 0.3 seconds, or less than 0.1 seconds.This time responsiveness represents the delay or time lag between ameasured change in cumulative airflow and a corresponding change invapor output, based on modifying the power supplied to the heater toreflect the current puff volume. (There is initial time lag of about 0.7seconds in FIG. 7 for the cumulative vapor output to follow thecumulative airflow volume, but this represents the thermal inertia ofthe heater, rather than a time delay in the control loop). Accordingly,the linkage between puff volume and vapor output is readily apparent tothe user, who is therefore able to learn quickly how to exploit thisfunctionality of the device.

Furthermore, the approach described herein can be extended to a range ofelectronic vapor provision systems, such as heat-not-burn devices (whichmay include some plant matter or extract, for example, tobacco leaf,which is then heated or provided with steam to produce the desiredvapor). One example of such an alternative form of electronic vaporprovision system is described in US 2011/0226236, which discloses aninhaler containing an evaporator based on a composite planar structurethat incorporates both a heating mechanism and wicking mechanism. Such asystem provides high specific evaporative capacity for intermittentoperation, combined with high evaporator (vaporizer) efficiency. Such asystem may further include a pressure or airflow sensor for measuringairflow, and a control unit for controlling the power supplied to theheating mechanism in accordance with the approach described herein.

In order to address various issues and advance the art, this disclosureshows by way of illustration various embodiments in which the claimedinvention(s) may be practiced. The advantages and features of thedisclosure are of a representative sample of embodiments only, and arenot exhaustive and/or exclusive. They are presented only to assist inunderstanding and to teach the claimed invention(s). It is to beunderstood that advantages, embodiments, examples, functions, features,structures, and/or other aspects of the disclosure are not to beconsidered limitations on the disclosure as defined by the claims orlimitations on equivalents to the claims, and that other embodiments maybe utilized and modifications may be made without departing from thescope of the claims. Various embodiments may suitably comprise, consistof, or consist essentially of, various combinations of the disclosedelements, components, features, parts, steps, means, etc other thanthose specifically described herein. The disclosure may include otherinventions not presently claimed, but which may be claimed in future.

1. An electronic vapor provision system including: a vaporizer forvaporizing liquid for inhalation by a user of the electronic vaporprovision system; a power supply comprising a cell or battery forsupplying power to the vaporizer; a sensor for measuring the rate ofairflow through the electronic vapor provision system as a result of aninhalation by the user; and a control unit for iteratively controllingthe power supplied to the vaporizer for the inhalation by the user,wherein the electronic vapor provision system is adapted to, for eachiteration within the inhalation: measure the current airflow rate;update a cumulative airflow by summing the measurements of currentairflow rate by the sensor so far during the inhalation; and control, bythe control unit, the power supplied to the vaporizer based on theupdated cumulative airflow for this iteration and a desired relationshipbetween the cumulative airflow for the inhalation and amount of vaporoutput to the user for the inhalation; thereby allowing the user controlover the amount of vaporized liquid obtained in a given inhalation basedon the cumulative airflow for the given inhalation.
 2. The electronicvapor provision system of claim 1, wherein the vaporizer is a heaterwhich is supplied with power from the power supply to heat and therebyvaporize the liquid for inhalation by a user.
 3. The electronic vaporprovision system of claim 2, wherein the control unit controls the powersupplied to the heater to control the temperature of the heater.
 4. Theelectronic vapor provision system of claim 1, wherein the liquid isnicotine.
 5. The electronic vapor provision system of claim 1, whereinthe sensor for measuring the rate of airflow measures a pressure drop,and the control unit estimates a measured airflow rate from the measuredpressure drop.
 6. The electronic vapor provision system of claim 1,wherein the control unit determines the cumulative airflow based on themeasurements of airflow rate by the sensor.
 7. The electronic vaporprovision system of claim 1, wherein the control unit is configured sothat a cumulative vapor output is maintained approximately proportionalto the cumulative airflow.
 8. The electronic vapor provision system ofclaim 1, wherein the system controls the power supplied to the vaporizerbased on (i) the measured airflow rate A(t), (ii) the desiredrelationship between the cumulative airflow for the given inhalation andthe amount of vaporized liquid provided to the user for the giveninhalation, and (iii) a system relationship between the power input tothe vaporizer and the amount of vaporized liquid produced by thevaporizer.
 9. The electronic vapor provision system of claim 1, whereinthe system controls the power supplied to the vaporizer based at leaston a predicted cumulative airflow, wherein the predicted cumulativeairflow is derived from the measured rate of airflow for the giveninhalation and a predetermined model for the puff profile.
 10. Theelectronic vapor provision system of claim 1, wherein the systemcontrols the power supplied to the vaporizer to provide the user with areal-time response in terms of amount of vapor output with respect tothe cumulative airflow for the inhalation by the user.
 11. Theelectronic vapor provision system of claim 10, wherein the systemcontrols the power supplied to the vaporizer to provide the user with areal-time response of 0.3 seconds or less.
 12. A method of operating anelectronic vapor provision system including a vaporizer for vaporizingliquid for inhalation by a user of the electronic vapor provisionsystem; a power supply comprising a cell or battery for supplying powerto the vaporizer; a sensor and a control unit for iterativelycontrolling the power supplied to the vaporizer for an inhalation by auser, said method comprising, for each iteration within the inhalation:measuring, by the sensor, the current airflow rate through theelectronic vapor provision system as a result of the inhalation by theuser; updating a cumulative airflow by summing the measurements ofcurrent airflow rate by the sensor so far during the inhalation; andcontrolling, by the control unit, the power supplied to the vaporizerbased on the updated cumulative airflow for this iteration and a desiredrelationship between the cumulative airflow for the inhalation by theuser and amount of vapor output to the user for the inhalation; therebyallowing the user control over the amount of vaporized liquid obtainedin a given inhalation based on the cumulative airflow for the giveninhalation.
 13. (canceled)
 14. (canceled)